Common vtable format for all variables
Maintainer: Dan Sugalski <dan@sidhe.org> Class: Internals PDD Number: 2 Version: 1 Status: Developing Last Modified: 05 February 2001 PDD Format: 1 Language: English
None. First version
This RFC presents the vtable entries, and their order, that all variables MUST provide.
All perl variables hide their guts behind a magic perl structure generally referred to as a PMC, or Perl Magic Cookie. Nothing outside the core of perl (in fact, nothing outside the data type's vtable routines) should infer anything about a PMC. (hence the Magic part)
The first parameter to all of these should be the destination PMC.
vtables are neat because they decouple the interface and implementation of various object functions. This does mean, though, that you need to either know what functions are available and what they do, or have some method of finding out. It's faster if you know which vtable entry does what, so that's the method perl's using.
For ease of use, we define the following semi-abstract data types
This is a generic integral value
This is a generic floating point value
This is a generic string value
This is a generic boolean value
See the PDD specifying perl's internal data types for more details, but in a nutshell they are:
This is a platform-native integer. Probably 32 or 64 bits, though there's no guarantee made.
This is perl's big integer format. It's an infinite (more or less, until you run out of memory) precision integer.
The platform-native floating point value. Probably around 80 bits (with 53 bits of precision) though that will vary from system to system.
Perl's big floating point format. Again potentially infinite precision, within the limits of available memory.
All perl strings are counted, of course, so we don't have any forbidden characters and take steps against buffer overruns reasonably easily.
This is a buffer of binary data. Perl makes no assumptions about its contents, and won't ever implicitly translate it to any other representation.
This is a Unicode string in UTF-32 format.
This is a string in platform native format.
This is a string in a non-native format for the platform that perl still knows how to deal with.
The following functions are defined:
IV type(PMC[, subtype]); STR name(PMC[, key]); void new(PMC[, key]); void clone(PMC, PMC[, flags[,key]); void morph(PMC, type[, key]); BOOL move_to(void *, PMC); IV real_size(PMC[, key]); void destroy(PMC[, key]); INT get_integer(PMC[, key]); ## NUM get_number(PMC[, key]); ## STR get_string(PMC[, key]); ## BOOL get_bool(PMC[, key]); ## void * get_value(PMC[, key]); BOOL is_same(PMC, PMC[, key]); void set_integer(PMC, INT[, key]); ## void set_number(PMC, NUM[, key]); ## void set_string(PMC, STR[, key]); ## void set_value(PMC, void *[, key]); void add(PMC, PMC, PMC[, key]); ## void subtract(PMC, PMC, PMC[, key]); ## void multiply(PMC, PMC, PMC[, key]); ## void divide(PMC, PMC, PMC[, key]); ## void modulus(PMC, PMC, PMC[, key]); ## void concatenate(PMC, PMC, PMC[, key]); ## BOOL is_equal(PMC, PMC[,key]); ## void logical_or(PMC, PMC, PMC[, key]); ## void logical_and(PMC, PMC, PMC[, key]); ## void logical_not(PMC, PMC[,key]); ## void match(PMC, PMC, REGEX[, key]); void repeat(PMC, PMC, PMC[, key]); ## void nextkey(PMC, PMC, start_key[, key]); BOOL exists(PMC[, key]);
All the functions marked with ## must have multiple forms, one for each possible form of a data type. (IV, bigint, etc) Perl will automatically produce conversion code if a v it isn't.
void * get_value(PMC[, key]);
Returns a pointer to the beginning of currently "OK" data; the type of this data must be determined by examining the PMCs type. This must only be used by other vtable functions inside the core, and must never be used if the PMC is of a type defined by a user outside the core, unless you know what you're doing. (eg, comparing get_values from two PMCs of the same type, or set_value(PMC1,get_valu
type
get_value
set_value(PMC1,get_valu
WHERE IS THE REST OF THIS FILE?
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cpanm
cpanm Scheme
CPAN shell
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